The present invention relates generally to capillary or restrictors employed in refrigeration systems, and more particularly to a restrictor that can be adjusted to alter the refrigerant flow therethrough. It is desirable that a restrictor having a precise refrigerant flow be designed for a specific refrigeration system so as to provide the specific flow characteristics required by the system.
In employing capillary tubes as restrictors between the high pressure and low pressure sides of the refrigeration system, the passageway through the restrictor must be specifically designed and sized for the system and cannot be altered by a service man in the field if operating conditions warrant it. The alternative in many instances is to replace it with another restrictor also having a predetermined flow characteristic.
It is also desirable in refrigerator systems that the restrictors be designed so that saturation conditions are maintained throughout the entire evaporator while permitting the suction line to superheat in order to prevent flooding of the compressor.
In U.S. Pat. No. 3,967,489-Pohl, assigned to the General Electric Company, the assignee of the present invention, a restrictor is provided that is shaped while the flow fluid passing therethrough is measured so that a restrictor having a specific predetermined flow characteristic is provided. The shaped restrictor is then installed as part of a refrigeration system requiring that particular flow characteristic. In practice, however, the refrigeration system including the restrictor having the predetermined flow characteristics as employed in a particular self-contained air conditioner might not operate at its optimum level after the unit is stabilized under full load conditions. It may be advantageous to provide restrictors that are capable of varying the refrigerant flow between the condenser and evaporator relative to the operating conditions of the system. This is especially true when the same refrigeration system is employed in air conditioning units having air flow systems that provide different air flow characteristics from one unit to the next. Adjustable restrictors are also utilized to provide refrigeration systems that function efficiently over a wide range of ambient temperatures.
In some instances expansion valves are employed that automatically adjust the flow of liquid refrigerant to the evaporator to balance compressor pumping capacity during a wide range of conditions. However, the devices are expensive in that the operating components are generally machined to function at relatively close tolerances.
U.S. Pat. No. 2,227,537 provides an elongated passage formed of a long strip of thin metal which is provided with a groove. The strip may then be folded upon itself, or a second sheet of metal may be placed at the edges to isolate the passage, and then rolled into a spiral. The initial restriction provided in the passage may be controlled by varying the radius of curvature and the amount of curl of the assembled sheet metal portions.
U.S. Pat. No. 2,532,452--Holsel provides a coupling including a ferrule having an initial bore that slip fits over the tube. Securing the coupling effectively compresses the ferrule and reduces the initial bore of the ferrule. This reduction in the initial bore squeezes the outside diameter of the tube at that part and accordingly reduces the passageway of the tube.